In tractors and other equipment with hydraulic power systems for operating auxiliary units, it is frequently desirable to provide more outlets for the hydraulic system than those with which the original equipment was supplied. Conventionally, this involves plumbing in one or more additional hydraulic circuits, including extra hydraulic lines and control valves at the operator's station, e.g. in the cab of a tractor. The conversion is time consuming and costly and the potential leak points are multiplied.